In many situations, people use systems to thwart off enemies like thieves, robbers and rapists.

-For the home, there's all kinds of alarm systems.

-For the woman walking through the ghetto late at night, there's the no-contact electro-shock jacket,
which fends off rapists.

-For shops and banks, there's the video-camera system.

In many of these situations, you fended the criminal off, but you never know who really attacked you. You may have captured his (masked) body on a camera, but you're not sure who it is.

Police and prosecuters have to establish "beyond a reasonable doubt" whether the suspect they're holding is the real one. Genetic evidence is great, but often difficult to obtain.

Now here come in the CrimeTags. They're basically the opposite of genetic traces: if the criminal doesn't leave traces on you or your property, you or your property leave traces on them.
These microscopic particles are sprayed onto the non-suspecting criminal so that he can be identified with 100% certainty at a later date. This dust carries information.

The characteristics of these particles are:

-They stick not only to clothes, but they attach themselves to the skin: if you try to rub them off, they bury themselves deeper into the skin and the clothes. (You can easily create these, mimicking certain seeds with this quality, which can be found in nature; they stick and bury themselves into the skin of animals who carry them along for days. And it's very difficult to wash them off.)

-They are coded; these dust tags have a special unique code, with which you can establish beyond a reasonable doubt that this particular person was present at this particular spot.

The potential applications are manifold:

-home alarm systems
-no contact jackets which spew out a fine dust
-military: targetbomb clouds of dust onto militias in Najaf, so that you can establish at a later date that these persons were at this particular spot, and are enemy combattants, beyond a reasonable doubt
-car security, etc...

They would come in handy when genetic evidence is of questionable quality, or when other dust particles (from carpets, etc) are too common to establish 100% sure that the criminal was in your home.

[DrC] with a dye the perpetrator knows
he's marked and may have a chance to
remove the evidence, given time. He
might not think about it with a non-
obvious taggant. Also, [django] points
out there are other possible
applications which would not work with
a dye.

Another tagging system is called the "Bullet." These are very hard to remove without medical experts, who are required by law to report the incident.

Sadly, there are a lot of laws about the use of these tagging devices, and their delivery system.

Perhaps a toned down shotgun shell, filled with those little "explosive" tags would be of some use. Not enough to really kill, or even seriously maim, but it would spit them out fast enough to get through the perp's skin.

There would probably be a lot of laws about that too, and apparently any device designed to do this would be a legal nightmare, so the homeowner would have to shoot them themselves, and if it came to that, as a home owner, I would prefer to use something a little more substantial.